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UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

IN 

PSYCHOLOGY 


Vol.  1,  No.  5,  pp.  323-344 


March  3,  1916 


DIURNAL  VARIATIONS  IN  MEMORY 
AND  ASSOCIATION 


BY 


ARTHUR  I.  GATES 


o 
>- 


UNIVERSITY  OF  CALIFORNIA  PRESS 
BERKELEY 


334     University  of  California  Publications  in  Psychology    [Vol. 


TABLE  V 

The  Absolute  and  Relative  Mean  and  Median  of  Figures  Recognized 
(Penalized  Score) 
a.m.  P.M. 


Hour 8:30       9:30     10:30     11:30       1:30       2:30       3:30       4:30       5:30 

A  v.  No. 

recognized  10.8  12.5  13.2  12.5  11.5  12.0  13.0  13.0  12.8 
Mean 

variation  2.0         1.9         1.9         1.8         1.9         1.8         1.8         2.1         2.0 

Mean, 

percent....    100.0     115.7     122.2     115.7     106.5     111.0     120.0     120.0     118.5 

Median 11.1       12.0       13.0       12.3       10.6       11.0       13.0       13.5       13.0 

Median, 

percent....     100.0     108.0     117.0     112.0       96.4       99.0     117.0     121.0     117.0 


A.M. 


P.M. 


Hour     8:30         9:30       10:30       11:30        1:30         2:30         3:30         4:30       5:30 


Mean. 


Median 

Fig.  5. — The  diurnal  course  of  recognition  of  figures. 
(Penalized  score) 

The  figures,  relatively,  are  not  greatly  changed  by  penalizing 
the  subjects  for  erroneous  recognitions.  11 :  30  a.m.,  by  virtue  of 
fewer  errors,  shows  a  slightly  higher  efficiency,  while  5:30  p.m., 
on  account  of  more  frequent  errors,  shows  less  relative  efficiency 
than  before.  The  mean  variations  of  the  two  last  hours  of  the 
day  remain  high.  The  changes  brought  about  by  penalizing  the 
subjects  for  errors  have  resulted  in  making  the  curves  correspond 
more  closely  than  formerly  to  the  curves  of  functions  considered 
earlier. 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     335 

Table  VI  shows  the  amount  of  errors  made  at  different  hours 
of  the  day,  without  regard  to  the  total  amount  of  correct  recog- 
nitions. The  percentage  columns  show  efficiency  and  do  not  show 
the  relative  number  of  errors ;  i.e.,  the  larger  this  percentage,  the 
fewer  the  errors.4 

TABLE  VI.  EEROES  IN  RECOGNITION 

Showing  the  Mean  and  Median  Errors  Made,  with  the  Eelative 
Efficiency  at  Each  Hour 
a.m.  p.m. 

Hour 8:30       9:30     10:30     11:30       1:30       2:30       3:30       4:30       5:30 

A  v.  No. 
errors 2.31       2.04       1.78       1.93       2.16       2.40       1.90       3.06       2.50 

variation        1.13       1.40       1.22       1.76       1.45       1.48       1.27       1.82       1.95 

Eelative 

efficiency    100.0     112.0     130.0     120.0     107.0       96.3     121.5       75.5       92.5 
Median 2.00       2.00       1.50       1.50       1.80       2.15       1.32       2.30       2.00 

Eelative 

Median 100.0     100.0     133.0     133.0     111.0       93.0     151.5       87.0     100.0 

A.M.  P.M. 

, K * 

Hour     8:30         9:30       10:30       11:30        1:30         2:30         3:30         4:30       5:30 


Mean.... 


Median 


Fig.  6. — The  diurnal  course  of  efficiency  with  regard  to  decrease 
of  erroneous  recognitions 


4  The  figures  showing  the  relative  efficiency  are  obtained  by  dividing 
the  score  for  eight  o'clock  by  the  score  for  any  particular  hour. 


EDUCATION  DEPT. 


UNIVERSITY  OF  CALIFORJ^A  PUBLl£AXjQ**si  •/« 

IN 

PSYCHOLOGY 

Vol.  1,  No.  5,  pp.  323-344  March  3,  1916 


DIURNAL  VARIATIONS   IN   MEMORY 
AND  ASSOCIATION 


BY 

AETHUR  I.  GATES 


I.  The  Problem  and  the  General  Method  op  Procedure 

A  year  ago,  the  writer  attempted  to  summarize  the  more  im- 
portant results  obtained  by  earlier  investigators  on  the  problem  of 
diurnal  variations  in  efficiency,  adding  certain  experimental  find- 
ings of  his  own  obtained  by  tests  upon  school  children.  A  more 
extended  discussion  of  the  problem,  its  significance,  and  diffi- 
culties will  be  found  in  that  article.1 

The  present  investigation  differs  from  the  earlier  one  in  several 
respects.  In  the  present  work  adults  served  as  subjects  in  the 
tests,  which  were  extended  over  a  greater  portion  of  the  day  than 
previously.  In  the  first  investigation,  moreover,  tests  for  a  variety 
of  mental  and  motor  functions  were  employed,  while  in  the 
present  work  the  tests  are  all  included  in  the  general  field  of 
memory  and  association. 

One  hundred  and  sixty-five  college  students,  members  of  a  class 
in  elementary  psychology,  served  as  subjects  for  the  experiments. 
Three  full  days  were  required  to  complete  the  experiments.  The 
temperature  on  the  particular  days  chosen  varied  from  56  to  66 
degrees  Fahrenheit.    The  tests  were  given  to  groups,  each  includ- 


i  Variation  in  Efficiency  during  the  Day,  together  with  Sex  Differences, 
Practice  Effects,  and  Correlations,  Univ.  Calif.  Publ.  Psychol.,  vol.  2  (1916), 
no.  1. 


324   :^iiWWih^f'^lifA'm»,Publications  in  Psychology     [Vol.  1 

ing  from  six  to  fourteen  students  at  each  hour  of  the  day,  except 
from  noon  to  1:00  o'clock,  the  first  beginning  at  8:00  a.m.  and 
the  last  at  5 :  00  p.m.  The  subjects  were  seated  at  a  long  table,  at 
one  end  of  which  stood  the  experimenter.  The  tests  were  given 
in  the  order  in  which  the  results  are  presented  in  this  article.  The 
time  required  for  all  the  tests  of  any  single  sitting  was  about 
half  an  hour. 

For  the  purpose  of  gaining  fuller  information  with  regard  to 
his  habits  of  life  and  especially  of  variations  from  the  normal 
routine  of  the  day,  the  following  questionaire  was  filled  out  by 
each  student: 

1.  Name. 

2.  College  year. 

3.  Did  you  do  any  especially  hard  work  today?    What? 

4.  Did  you  do  any  especially  hard  work  just  before  this  hour?  What? 

5.  What  time  do  you  usually  go  to  bed? 

6.  What  time  do  you  usually  get  up? 

7.  Did  the  time  of  going  to  bed  last  night  or  the  time  of  getting  up 

this  morning  differ  from  the  average?    How  much? 

8.  Do  you  usually  eat  a  heavy  or  a  light  breakfast? 

9.  Do  you  usually  eat  a  heavy  or  a  light  lunch? 

10.  Any  exception  today  with  regard  to  meals? 

11.  What  hours  do  you  think  are  your  best  for  work  or  study? 

12.  What  are  your  reasons  for  believing  so? 

The  answers  to  question  7  showed  that  the  majority  of  these 
students  go  to  bed  at  10 :  30  or  11 :  00  o  'clock.  The  following 
table  shows  the  distribution : 

Hour  8:30       9:00       9:30     10:00     10:30     31:00     11:30     12:00 

No.  of  inds 1  8  24  43  71  64  22  7 

Per  cent  0.4         3.3       10.0       17.8       29.6       26.6         9.2       2.9 

The  following  table  shows  the  time  of  getting  up : 

Hour    5:00       5:30       6:00       6:30       7:00  7:30  8:00 

No.  of  inds 4            0          28          58          90  57  3 

Per  cent  1.6         0.0       11.6       24.2       37.4  23.7  1.2 

Seven  o'clock  is  the  favorite  hour  of  rising,  although  about 
one-fourth  arise  at  6 :  30  and  another  fourth  at  7 :  30. 

The  matters  of  chief  importance  in  this  connection  are  the 
departures  from  the  normal  habits  of  life  on  the  part  of  the  sub- 


19161   Gates:  Diurnal  Variations  in  Memory  and  Association     325 

jects.  Answers  to  2,  3,  7,  and  10  gave  the  information  with  regard 
to  such  departures.  In  most  cases  where  the  subject  had  gone  to 
bed  much  later  than  usual,  had  got  up  much  later  than  usual,  or 
missed  a  meal,  or  had  some  especially  hard  work  just  before  the 
test,  the  data  from  him  were  not  included. 

Following  are  the  chief  factors,  in  addition  to  those  just 
enumerated,  which  seemed  to  give  just  reason  for  discarding  a 
subject's  work :  (1)  Copying  from  others  or  using  unfair  methods 
of  any  sort,  although  such  cases  were  very  rare;  (2)  lack  of 
interest,  or  inattention;  (3)  physical  defects,  such  as  conspicuous 
defects  of  sight  or  hearing,  or  sickness,  bruised  fingers,  and  the 
like,  when  of  such  a  nature  as  to  interfere  with  maximal  perform- 
ance; (4)  failure  to  understand  directions,  etc.,  after  the  test  had 
been  started. 

On  the  whole,  however,  nearly  all  of  the  subjects  conformed 
to  all  the  rules  of  the  tests  and  the  results  were  considered  trust- 
worthy and  to  be  the  products  of  their  very  best  efforts.  Many 
minor  differences  among  the  individuals  existed  with  regard  to  the 
character  of  the  day 's  activity.  Some  had  many  and  some  had  few 
college  exercises  before  the  test;  some  had  done  more  and  some 
less  studying  than  usual.  The  possibilities  of  such  differences 
were,  of  course,  greater  for  those  coming  in  the  latter  part  of  the 
day;  but  except  for  reasons  mentioned  above,  the  data  from  all 
subjects  were  retained.  Perfect  conditions  would  consist  in  an 
identical  programme  for  the  day  for  all  the  subjects,  one  in  which 
very  little  or  no  fatiguing  work  was  done;  but  such  conditions 
could  not  be  obtained. 

The  following  table  shows  the  distribution  of  individuals 
according  to  their  preferred  hours  for  study  and  work : 


A.M. 

A. 

NOON 

Hour 

No.  of  inds. 

4:00 
2 

5:00 
17 

6:00 
36 

7:00       8:00 
42        109 

P.M. 

A. 

9:00 
137 

10:00 
87 

11:00 
38 

12:00 
5 

Hour 1:00   2:00   3:00   4:00   5:00   6:00   7:00   8:00   9:00 

No.  of  inds.     2     2     2    11    12     5    17    29   22 


10:00  11:00  12:00   No  preference. 
20     6     0        9  ' 


326      University  of  California  Publications  in  Psychology    IT0L- 1 

The  morning  hours  are  preferred  by  most  individuals,  with  the 
evening  hours  next  in  order.  Nine  a.m.  is  the  most  popular  hour, 
although  8  a.m.  is  preferred  by  nearly  as  many  persons.  Ten  a.m. 
follows  next  in  order  of  preference  and  6  and  7  a.m.  rank  higher 
than  the  best  afternoon  or  evening  hours.  Eight  p.m.  is  the 
preferred  evening  hour  and  4  and  5  p.m.  are  the  preferred  after- 
noon hours. 

The  reasons  given  by  the  subjects  for  believing  that  their  pre- 
ferred hours  are  really  their  best  hours  are  very  much  alike.  In 
almost  every  instance  the  reasons  amount  merely  to  an  opinion 
based  on  their  subjective  feelings.  An  effort  will  be  made 
in  this  work  to  discover  how  closely  the  curve  of  distribution  of 
preferred  hours  follows  the  curve  of  real  efficiency  as  shown  by 
the  experimental  findings.  For  the  morning  hours  the  reports  are 
of  this  sort :  "  I  feel  more  energetic ; "  ' '  I  am  in  better  condition, 
physically  and  mentally ;"  "My  mind  is  clearer;"  and  the  like. 
Those  who  prefer  the  afternoon  hours  report :  ' '  I  have  got  into 
the  swing  better;"  "I  am  more  wide-awake;"  and  so  on.  The 
statements  with  regard  to  the  evening  hours  are  much  the  same, 
although  those  preferring  the  late  evening  and  the  very  early 
morning  hours  attribute  their  greater  efficiency  to  the  existence 
of  fewer  distractions  at  those  times.  Many  admit  that  they  seem 
to  have  greater  success  at  a  particular  time  largely  because,  on 
account  of  the  force  of  circumstances  or  by  arbitrary  choice,  it 
had  become  habitual  for  them  to  do  their  hardest  work  at  those 
hours. 


II.  Tests  in  Auditory  Memory 

For  a  test  in  auditory  memory  the  following  series  of  digits 
were  used:  9627,  41852,  736294,  8513627,  38471629,  529468371. 
2574638197,  83519472631,  628194357283. 

Detailed  instructions  with  regard  to  the  method  of  conducting 
the  tests  were  given.  The  digits,  beginning  with  the  shortest 
series,  were  read  sharply  and  without  rhythm  at  the  rate  of  one 
each  three-fourths  of  a  second,  the  rate  being  fixed  by  a  silent 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     327 

pendulum  invisible  to  the  subjects.  The  tests  in  auditory  memory 
was  given  first  of  all  to  the  groups  on  the  first  two  days  of  the 
experiment,  and  second  (following  the  visual  series)  on  the  last 
day. 

The  results  are  given  in  terms  of  the  average  (mean)  spans 
with  the  mean  variation,  and  of  the  median  spans  of  the  indi- 
viduals in  the  different  groups.  By  the  "span"  is  meant  the 
longest  series  reproduced  correctly  in  toto.    But  in  case  a  series 


TABLE  I.     AUDITORY  MEMORY 

The  Absolute  and  Relative  Mean  and  Median  of  Digits  Reproduced 
at  Different  Hours 

A.M.  P.M. 

, A ,   i ■ ; 

Hour 8:00       9:00     10:00     11:00       1:00       2:00       3:00       4:00       5:00 

No.  of 

subjects....         23  23  28  28  25  25  25  30  25 

Av.  No. 

digits 7.81       7.61       7.72       8.08       7.60       7.38       7.67       7.46       7.33 

Moo-n 

variation        1.20  1.10  1.15       1.05       1.40  1.07  0.92       1.00       1.10 
JVTprh 

per  cent....  100.0  97.5  98.8     103.3       97.4  94.5  98.2       95.5       93.8 

Median 7.00  7.20  7.20       7.50       7.40  7.30  7.40       7.10       7.08 

Median, 

per  cent....  100.0  103.0  103.0     107.0     105.8  103.9  105.8     101.4     101.0 

A.M.  P.M. 

, * <  f » > 

Hour     8:00         9:00       10:00       11:00        1:00         2:00         3:00         4:00       5:00 
Mean.. 


Median 


Fig.  1. — Auditory  memory.2    The  diurnal  course  of  memory  for 
auditory  digits 


2  The  diagrams  are  based  on  the  percentage  columns  in  the  corespond- 
ing  tables. 


328      University  of  California  Publications  in  Psychology     IT0L- 1 

was  correctly  reproduced  entire,  following  two  or  more  incorrect 
series,  the  correct  series  preceding  the  failures  was  taken  as  the 
span.  Thus,  if  an  individual  reproduced  a  series  of  six  digits, 
failed  at  seven  and  eight,  succeeded  at  nine  and  failed  thereafter, 
the  series  of  six  digits  was  considered  the  span.  The  results  are 
given  in  Table  I. 

The  mean  and  the  median  both  show  a  marked  and  steady 
increase  in  efficiency  during  the  forenoon,  with  the  exception  that 
the  mean  for  8  o'clock  is  high  compared  to  that  for  9  or  10 
o'clock.  The  median  for  this  hour,  however,  is  lower  than  for 
any  other  forenoon  hour.  The  maximum  efficiency  for  the  day, 
according  to  both  methods  of  computation,  is  at  11  o'clock. 
Efficiency  at  1  o  'clock  is  lower  than  at  11  o  'clock  and  at  2  o  'clock 
it  is  still  lower,  whence  it  moves  upward  to  the  afternoon  maxi- 
mum at  3  o'clock.  According  to  the  median,  however,  3  p.m.  is 
equal  in  efficiency  to  1  p.m.  ;  and  although  the  mean  at  1  p.m.  is 
less  than  at  3,  it  is  greater  than  at  2  o'clock.  It  will  be  noticed, 
however,  that  the  mean  variation  is  greater  at  1  o'clock  than  at 
any  other  hour  of  the  day,  indicating  the  small  reliability  of  this 
measure.  In  general,  there  is  a  steady  and  pronounced  increase 
in  efficiency  during  the  forenoon,  a  fall  following  the  lunch  hour, 
an  increase  at  3  p.m.,  and  a  final  drop  at  the  end  of  the  day. 

III.  Tests  in  Visual  Memory 

The  following  series  of  digits  were  used  as  tests  of  visual 
memory:  6283,  57294,  241738,  2170463,  27986543,  215903847, 
5978024318,  57402623871,  183570467392.  The  displays  were 
made  up  of  black  gummed  digits  two  and  three-fourths  inches  in 
height,  pasted  on  white  cards  two  and  a  half  by  three  and  a  half 
inches  in  size,  which  were  pasted  in  series  on  a  strip  of  gray  cloth. 

The  strips  were  exposed  in  order  of  length,  beginning  with  the 
series  of  four  digits.  The  folded  strip  was  held  before  the  sub- 
jects, the  word  "ready"  was  given  and  the  strip  was  drawn  taut 
with  a  snap,  exposing  the  series.  The  subjects  wrote  the  digits 
as  soon  as  the  strip  was  taken  from  sight.    The  time  of  exposure 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     329 

varied  with  the  length  of  the  series,  being  determined  by  multi- 
plying the  number  of  digits  in  each  series  by  three-fourths  of 
a  second. 

The  method  of  treating  the  data  and  computing  the  results 
was  the  same  as  that  employed  in  the  tests  of  auditory  memory. 
The  results  are  stated  in  the  absolute  and  relative  number  of 
digits  reproduced,  determined  by  the  arithmetical  mean  and 
median. 

TABLE  II.     VISUAL  MEMOKY 

The  Absolute  and  Kelative  Mean  and  Median  of  Digits  Reproduced 
at  Different  Hours 

a.m.  P.M. 

A A 

Hour 8:00       9:00     10:00     11:00       1:00       2:00       3:00       4:00       5:00 

No.  of 

subjects....         23  24  28  24  24  25  26  26  25 

Av.  No. 

digits 8.00       7.95       8.14       8.14       7.84       8.08       8.15       8.17       8.00 

variation        1.25       1.13       1.06       1.19       1.20       1.30       1.08       1.16       1.20 

per  cent....  100.0  99.3  101.5  101.5  98.0  100.1  101.7     102.0  100.0 

Median 7.50  7.50       7.70  7.60  7.25  7.50  7.80       7.60  7.50 

Median, 

percent....   100.0  100.0  103.0  101.5  96.7  100.0  104.0     101.5  100.0 

A.M.                                                                                P.M. 
A A 

Hour  8:00  9:00  10:00  11:00  1:00  2:00  3:00  4^00  5-00 
Mean.. 


Median 


Fig.  2. — The  diurnal  course  of  visual  memory 


In  many  respects  the  course  of  efficiency  in  memory  for  visual 
digits  is  the  same  as  for  auditory  digits.  The  general  increase 
in  efficiency  during  the  forenoon  is  evident,  although  the  same 


330      University  of  California  Publications  in  Psychology     [Vol.  1 

exception  is  found  with  regard  to  the  8  o'clock  hour — i.e.,  a 
superiority  of  that  hour  over  9  o  'clock,  as  shown  by  the  mean  but 
not  by  the  median.  In  the  case  of  visual  memory,  however, 
11  a.m.  is  barely  equal  to  10  a.m.  according  to  the  mean,  and  is 
slightly  inferior  according  to  the  median.  In  the  afternoon,  from 
the  fall  at  1  p.m.  there  is  a  steady  increase  in  efficiency  until 
3  p.m.,  as  shown  by  the  median ;  and  the  mean  indicates  that  this 
increase  persists  until  4  p.m.  Both  measures  show  a  decrease  in 
efficiency  following  4  o  'clock.  On  the  whole,  there  is  a  high  degree 
of  correspondence  between  the  curves  for  the  two  forms  of 
memory  for  digits. 

IV.  Substitution  Test 

For  a  test  in  the  rapidity  of  learning,  a  form  of  code  was 
used.3  This  test  gives  a  fair  measure  of  the  rapidity  with  which 
associations  are  formed  by  repetition.  The  associations  consist  in 
the  formation  of  connections  between  a  series  of  nine  symbols 
and  nine  digits,  and  are  established  gradually  as  the  test  proceeds. 

The  material  consisted  of  printed  cardboard  "key"  forms, 
three  by  seven  inches,  containing  nine  circles,  in  each  of  which 
was  enclosed  the  symbol  and  the  corresponding  digit;  and  also 
of  test  sheets  eight  and  a  half  by  eleven  inches  in  size,  on  each 
of  which  were  printed  two  columns  of  twenty-five  rows  of  five 
symbols  each,  with  blank  spaces  to  correspond.  Altogether,  each 
sheet  contained  250  symbols  and  250  blank  spaces. 

The  test  sheets  and  the  keys  were  passed  to  the  subjects,  the 
keys  face  downward  and  the  test  sheets  face  upward  in  proper 
position.  The  method  of  conducting  the  test  was  then  explained 
in  detail.    Six  minutes  were  allowed  for  the  work. 

The  test  sheets  were  checked  up  for  errors  and,  excluding 
them,  the  total  number  of  digits  written  was  computed.  The 
results  are  given  in  Table  III. 

Again  an  increase  in  efficiency  during  the  forenoon  is  found, 
although  11  o'clock  is  slightly  inferior  to  10  o'clock.    The  after- 


3  For  a  discussion  of  this  test,  see  Whipple,  G.  M.,  Manual  of  Physical 
and  Mental  Tests  (1910),  pp.  350  ff. 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     331 

noon  maximum  stretches  from  2  to  4  o  'clock,  the  figures  for  these 
hours  being  nearly  the  same.  The  hours  of  lowest  efficiency  for 
the  day  are  1  p.m.  and  5  p.m.,  the  latter  being  slightly  below  the 
former.  The  curve,  in  a  general  way,  is  very  closely  akin  to  those 
found  for  the  previous  functions. 

TABLE  III.     SUBSTITUTION  TEST 
The  Absolute  and  Eelative  Mean  and  Median  for  Different  Hours 

A.M.  P.M. 

Hour 8:25       9:25     10:25     11:25       1:25       2:25       3:25       4:25       5:25 

No.  of 
subjects....         18  23  25  23  19  23  27  24  21 

Av.  No. 
digits 174.0     179.0     183.4     181.8     167.0     179.0     177.0     176.6     164.0 

Mean 
variation  33  30  31  27  30  31  33  34  31 

percent....  100.0  102.7  105.2  104.3  96.0  102.6  101.5  101.2  94.3 

Median 174.0  176.0  181.0  180.0  166.0  169.0  170.0  170.0  165.5 

Median, 

percent....  100.0  101.2  104.0  103.4  95.5  97.2  97.7  97.7  95.3 


A.M.  P.M. 

A A. , — ^ 

Hour    8:25         9:25       10:25       11:25  1:25         2:25         3:25         4:25       5:25 
Mean.... 


Median 


Fig.  3. — The  diurnal  course  of  efficiency  in  the  substitution  test 

V.  Tests  in  Recognition 
The  material  consisted  of  a  sheet  of  twenty-five  geometrical 
figures  for  a  learning  series  and  a  larger  sheet  containing  the 
original  twenty-five  figures  mixed  indiscriminately  with  twenty- 
five  new  figures  for  a  test  series.    The  subjects  marked  off  on  the 


332      University  of  California  Publications  in  Psychology     [Vol.  1 

test  sheet  the  recognized  figures.  No  one  succeeded  in  recognizing 
all  of  the  figures,  and  very  few  completed  the  tests  without 
erroneous  recognitions. 

The  method  of  conducting  the  test  was  explained  in  detail  and 
both  sheets  were  passed  out  face  downward.  One  minute  was 
allowed  for  the  study  period  and  two  minutes  for  the  recognition 
work. 

TABLE  IV.     RECOGNITION  TEST 

The  Absolute  and  Relative  Mean  and  Median  of  Figures  Correctly 

Recognized 

p.m. 


A.M. 

— a 


Hour 8:30       9:30     10:30     11:30       1:30       2:30       3:30       4:30       5:30 

No.  of 

subjects....       21  24         29         28  24         25         27         29  22 

Av.  No. 

recognized     13.1       14.5       15.1       14.3       13.6       14.0       15.3       16.3       16.3 
Mean 

variation  2.5         2.8         2.7         2.0         2.1         2.3         2.2         3.1         3.3 

percent....  100.0  111.5  115.0  109.0  104.0  107.0  116.8  124.5  124.5 

Median 11.7  15.0  15.0  14.5  12.5  14.2  15.2  16.1  16.0 

Median, 

percent....  100.0  128.0  128.0  124.0  107.0  121.0  130.0  137.5  136.6 


A.M. 


Hour     8:30         9:30       10:30       11:30        1:30         2:30         3:30         4:30       5:30 


Mean- 


Median 


Fig.  4. — The  diurnal  course  of  efficiency  for  recognition  of  figures 


19161   Gates:  Diurnal  Variations  in  Memory  and  Association     333 

The  data  were  scored  by  counting  the  number  of  figures  cor- 
rectly cancelled  and  the  number  incorrectly  cancelled.  Twenty- 
five  would  be  a  perfect  score.  The  results  have  been  computed, 
first,  on  the  basis  of  the  number  of  figures  correctly  cancelled; 
second,  on  the  basis  of  a  penalized  score  in  which,  from  the  num- 
ber correctly  recognized,  one  credit  is  deducted  for  each  erroneous 
recognition;  and  finally,  tabulations  have  been  made  of  the 
number  of  errors  occurring  at  each  hour. 

Table  IV  gives  the  results  according  to  the  first  method  of 
computation. 

The  main  features  of  the  curves  for  efficiency  in  the  recog- 
nition of  figures  are  the  same  as  those  found  for  the  functions 
previously  considered.  The  differences  from  hour  to  hour,  especi- 
ally those  chosen  by  the  median,  are  exceedingly  great,  the  relative 
differences  being  here  many  times  greater  than  those  found  in  the 
memory  tests.  Both  mean  and  median  agree  in  showing  a  large 
and  steady  increase  during  the  forenoon,  which  has  ceased,  how- 
ever, by  11 :  30  a.m.  Compared  to  the  efficiency  of  the  morning 
hours,  a  decided  drop  is  evident  at  1 :  30  p.m.,  which  is  followed 
by  a  steady  increase  until  4 :  30  p.m.  ;  5 :  30  p.m.,  although  lower 
on  the  curve  than  4 :  30  p.m.,  is  still  very  high,  but  it  will  be  noted 
that  the  mean  variations  for  the  last  hours  are  very  high.  On  the 
whole,  there  is  a  high  correspondence  between  the  general  form 
of  the  curves  for  this  function  and  those  previously  considered. 

Table  V  gives  the  results  when,  from  the  scores  just  con- 
sidered, one  credit  was  deducted  for  each  erroneous  recognition. 
It  is  very  probable  that  this  arbitrary  method  may  give  a  good 
index  of  the  real  efficiency  of  many  individuals.  Some  subjects 
work  cautiously,  making  but  few  erroneous  judgments.  Others 
are  less  careful,  marking  out  almost  any  figure  which  seems  at  all 
familiar;  and,  by  increasing  the  number  of  cancellations,  mark 
out  a  greater  number  of  the  proper  figures,  in  many  cases  by 
mere  chance,  since  the  numbers  of  right  and  wrong  figures  were 
equal.  The  arbitrary  penalty  has  for  its  basis  the  fact  of  equal 
distribution  of  right  and  wrong  figures,  and  one  credit  is  there- 
fore deducted  for  each  error. 


334      University  of  California  Publications  in  Psychology     [Vol.  1 


TABLE  V 

The  Absolute  and  Eelative  Mean  and  Median  op  FiCxUkes  Becognized 
(Penalized  Score) 


a.m. 


Hour 8:30       9:30     10:30     11:30       1:30       2:30       3:30       4:30       5-30 

A  v.  No. 

recognized  10.8  12.5  13.2  12.5  11.5  12.0  13.0  13.0  12.8 
Mean 

variation  2.0         1.9         1.9         1.8         1.9         1.8         1.8         2.1         2.0 

Mean, 

percent....    100.0     115.7     122.2     115.7     106.5     111.0     120.0     120.0     118.5 

Median 11.1       12.0       13.0       12.3       10.6       11.0       13.0       13.5       13.0 

Median, 

percent....     100.0     108.0     117.0     112.0       96.4       99.0     117.0     121.0     117.0 


Mean.... 


A.M. 


P.M. 


Hour     8:30         9:30       10:30       11:30        1-30         2:30         3:30         4:30       5:30 


Median 

Fig.  5. — The  diurnal  course  of  recognition  of  figures. 
(Penalized  score) 

The  figures,  relatively,  are  not  greatly  changed  by  penalizing 
the  subjects  for  erroneous  recognitions.  11 :  30  a.m.,  by  virtue  of 
fewer  errors,  shows  a  slightly  higher  efficiency,  while  5:30  p.m., 
on  account  of  more  frequent  errors,  shows  less  relative  efficiency 
than  before.  The  mean  variations  of  the  two  last  hours  of  the 
day  remain  high.  The  changes  brought  about  by  penalizing  the 
subjects  for  errors  have  resulted  in  making  the  curves  correspond 
more  closely  than  formerly  to  the  curves  of  functions  considered 
earlier. 


1916]   Gates :  Diurnal  Variations  in  Memory  and  Association     335 

Table  VI  shows  the  amount  of  errors  made  at  different  hours 
of  the  day,  without  regard  to  the  total  amount  of  correct  recog- 
nitions. The  percentage  columns  show  efficiency  and  do  not  show 
the  relative  number  of  errors ;  i.e.,  the  larger  this  percentage,  the 
fewer  the  errors.4 

TABLE  VI.  EEEOES  IN  RECOGNITION 

Showing  the  Mean  and  Median  Errors  Made,  with  the  Relative 
Efficiency  at  Each  Hour 
a.m.  P.M. 

f A .  A 

Hour 8:30       9:30     10:30     11:30       1:30       2:30       3:30       4:30       5:30 

A  v.  No. 
errors 2.31       2.04       1.78       1.93       2.16       2.40       1.90       3.06       2.50 

variation        1.13  1.40  1.22       1.76  1.45  1.48       1.27       1.82  1.95 
Relative 

efficiency    100.0  112.0  130.0     120.0  107.0  96.3     121.5  75.5  92.5 

Median 2.00  2.00  1.50       1.50  1.80  2.15       1.32       2.30  2.00 

Relative 

Median 100.0  100.0  133.0     133.0  111.0  93.0     151.5  87.0  100.0 

A.M.  P.M. 

A, K 

Hour     8:30         9:30       10:30       11:30        1:30         2:30         3:30         4:30       5:30 


Mean.... 


Median 


Fig.  6. — The  diurnal  course  of  efficiency  with  regard  to  decrease 
of  erroneous  recognitions 


4  The  figures  showing  the  relative  efficiency  are  obtained  by  dividing 
the  score  for  eight  o'clock  by  the  score  for  any  particular  hour. 


336      University  of  California  Publications  in  Psychology     [Vol.  1 

The  number  of  errors  made  seems  to  decrease  during  the  fore- 
noon, the  fewest  being  made  at  10 :  30  a.m.,  with  11 :  30  a.m.  next 
in  order.  During  the  afternoon  the  smallest  number  of  errors 
are  made  at  3 :  30  p.m.,  with  a  great  many  in  the  2 :  30  p.m.  hour. 
Although  the  results  are  very  irregular  and  the  mean  variations 
exceedingly  high,  there  is  a  slight  indication  that  the  hours  at 
which  the  smallest  number  of  errors  were  made  were  the  hours  of 
greatest  efficiency  otherwise. 

VI.  Tests  in  Logical  Memory5 

Tests  in  logical  memory,  or  memory  for  ideas,  have  long  been 
used  to  determine  individual  differences  in  mnemonic  efficiency, 
as  related  to  age,  sex,  training,  etc.  This  test  differs  from  the 
preceding  tests  of  memory  in  two  respects ;  first,  material  which 
forms  a  significant  whole  is  used  instead  of  a  series  of  discon- 
nected impressions ;  and  second,  the  reproduction  of  ideas  rather 
than  the  exact  reproduction  of  sensory  forms  is  required.  There- 
fore, this  is  called  a  test  of  logical  memory,  in  contrast  to  rote 
memory. 

One  of  the  familiar  texts  devised  by  Healy  was  used,  begin- 
ning "If  a  man  finds  that  his  house  is  on  fire,  he  should  look  to 
see  if  it  is  a  large  fire,  etc. '  '6  The  material  is  divided  into  twenty 
parts,  each  of  which  is  counted  one  detail,  or  ' '  idea. ' '  The  method 
of  conducting  the  test  was  carefully  explained.  The  material  was 
read  slowly,  and  ample  time  was  allowed  in  which  to  write  the 
details  remembered.  One  unit  of  credit  was  given  for  the  recall 
of  each  "idea";  thus  an  accurate  reproduction  of  all  the  ideas 
would  give  a  score  of  twenty.    The  results  are  given  in  Table  VII. 

The  results  of  this  test  for  logical  memory  are  quite  irregular ; 
mean  and  median  do  not  harmonize  as  closely  as  usual.  The 
increase  in  efficiency  during  the  forenoon  which  has  generally 
been  found  to  be  the  rule,  does  not  appear  clearly  in  this  func- 


s  This  test  was  conducted  by  Miss  Ida  A.  Felt,  a  graduate  student  in 
psychology,  who  used  the  data  for  other  purposes. 

e  See  Healy,  W.,  and  Fernald,  G.  M.,  Tests  for  Practical  Mental  Classi- 
fications, Psych.  Monog.  (1911),  no.  54. 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     337 

TABLE  VII.     LOGICAL  MEMOEY 

The  Absolute  Mean  and  Median  of  the  Number  op  Ideas  Reproduced 
a.m.  P.M. 


Hour 8:40       9:40     10:40     11:40       1:40       2:40       3:40       4:40       5:40 

No.  of 

subjects....    22    23    27    28    22    22    25    28    26 
Av.  No. 

1 1 ideas' ' ....  13.20  14.40  14.20  13.60  12.60  13.10  13.40  13.50  12.05 
Mean 

variation   2.2    1.4    2.4    2.6    2.4    1.9    2.1    1.8    1.5 

per  cent....  100.0  109.0  107.7  103.0  95.5  99.3  101.4  102.2  91.3 

Median 13.5  14.5  14.0  14.2  13.5  13.5  14.0  13.5  12.6 

Median, 

per  cent....  100.0  107.3  103.7  105.1  100.0  100.0  103.7  100.0  93.3 


A.M. 


Median 


Fig.  7. — The  diurnal  course  of  efficiency  for  logical  memory 


tion.  The  maximum  of  the  day  appears  early,  at  9  :  40  a.m.  The 
mean  indicates  a  superiority  of  10 :  40  over  11 :  40  a.m.,  but  the 
median  shows  the  latter  hour  to  be  superior.  It  will  be  noted 
that  the  mean  variations  for  these  hours  are  very  large.  More 
uniform  and  more  characteristic  results  appear  in  the  afternoon 
curves.  The  mean  shows  an  increase  from  a  very  low  efficiency 
at  1 :  40  p.m.  to  an  afternoon  maximum  at  4 :  40.  The  latter  hour 
is,  however,  but  very  slightly  superior  to  3 :  40  p.m.  The  median 
indicates  a  maximum  for  the  afternoon  at  3  :  40  o  'clock.  The  final 
decrease  in  efficiency  at  5 :  40  is  clear  in  both  cases.     The  curves 


338      University  of  California  Publications  in  Psychology    [Vol.  l 

for  the  afternoon  hours,  then,  conform  fairly  closely  to  the  curves 
found  in  the  case  of  most  other  functions  previously  considered, 
but  with  regard  to  the  forenoon  hours  the  results  are  not 
harmonious. 

VII.  Summary  of  Results 

The  accompanying  table  and  figures  show  the  curves  for  the 
various  functions  that  have  been  considered,  grouped  for  pur- 
poses of  comparison.  The  mean  and  median  of  each  function  are 
given  as  percentages,  and  a  final  average  for  the  mean  and  median 
figures  of  all  functions  is  given. 

TABLE  IX.    ALL  FUNCTIONS 

The  Mean  and  Median,  per  cent,  for  the  Various  Functions 
a.m.  P.M. 

A f A. —^ 

Hour* 8:00  9:00  10:00  11:00  1:00  2:00  3:00  4:00  5:00 

Auditory  memory. 

Mean 100.0  97.5  98.8  103.3  97.4  94.5  98.2  95.5  93.8 

Median....    100.0  103.0  103.0  107.0  105.8  103.9  105.8  101.4  101.0 

Visual  memory. 

Mean 100.0  99.3  101.5  101.5  98.0  100.1  101.7  102.0  100.0 

Median....    100.0  100.0  103.0  101.5  96.7  100.0  104.0  101.5  100.0 

Substitution. 

Mean 100.0  102.7  105.2  104.3  96.0  102.6  101.5  101.2  94.3 

Median....    100.0  101.2  104.0  103.4  95.5  97.2  97.7  97.7  95.3 

Recognition.     (Penalized  score) 

Mean 100.0  115.7  122.2  115.7  106.5  111.0  120.0  120.0  118.5 

Median....    100.0  108.0  117.0  112.0  96.4  99.0  117.0  121.0  117.0 

Logical  memory. 

Mean 100.0  109.0  107.7  103.0  95.5  99.3  101.4  102.2  91.3 

Median....     100.0  107.3  103.7  105.1  100.0  100.0  103.7  100.0  93.3 

Averagef        100.0     104.3     106.6     105.6       98.7     100.6     105.1     104.2     100.4 

*  The  hours  at  which  the  series  of  tests  were  begun  is  given  here.  The 
actual  time  at  which  each  test  was  given  can  be  obtained  from  Tables  I  to 
VIII  above. 

f  Average  of  means  and  medians  of  all  functions. 

The  existence  of  many  irregularities  and  fluctuations  in  the 
various  curves  is  at  once  evident.  Yet  when  one  overlooks  these 
minor  differences,  it  can  be  seen  with  equal  clearness  that  there 


l916]   Gates:  Diurnal  Variations  in  Memory  and  Association     339 


A.M. 


P.M. 


Hour     8:00         9:00       10:00       11:00        1:00         2:00         3:00         4:00       5:00 
Auditory  memory. 

Mean . 


Median 


Visual  memory. 
Mean. 


Median 


Substitution 
Mean .... 

Median 
Recognition. 

Mean .... 

Median 
Logical  memory 

Mean .... 
Median 


Average 


Fig.  8. — All  functions.    Curves  based  on  Table  IX,  showing  the 
course  of  efficiency  for  all  functions 


340     University  of  California  Publications  in  Psychology     [Vol.  1 

is  throughout  a  great  similarity  in  the  general  form  of  the  curves. 
The  average  curve  shows  the  characteristic  trend  of  all  those  of 
which  it  is  made  up.  Beginning  at  8  a.m.  the  curve  moves 
steadily  upward  until  it  reaches  a  maximum  between  10  and  11 
o'clock.  In  the  average  curve,  10  o'clock  surpasses  11  o'clock 
slightly ;  a  fact  which  is  shown  by  some  of  the  individual  curves, 
while  others  show  the  opposite.  Compared  to  the  later  afternoon 
hours,  1  p.m.,  in  the  average  figure,  is  very  low;  in  fact,  it  is  the 
time  of  minimum  efficiency  of  the  day.  All  of  the  individual 
curves  agree  in  showing  1  o'clock  to  be  a  poor  hour.    From  the 

1  o  'clock  minimum,  the  average  curve  moves  upward  to  an  after- 
noon maximum  at  3  o'clock  and  then  tends  downward  again  until 
the  last  hour  of  the  day,  which  shows  an  efficiency  about  equal 
of  that  of  the  first  morning  hour.  There  are  many  departures 
from  the  central  tendency;  some  curves,  for  example,  show  an 
afternoon  maximum  at  3  o'clock,  others  at  4,  and  in  some  cases 

2  p.m.  stands  very  high ;  but  all  show  more  or  less  definitely  the 
characteristic  wave  of  efficiency. 

In  an  earlier  section  (p.  325),  a  table  was  made  showing  the 
distribution  of  the  individuals  taking  part  in  the  experiment 
according  to  their  preferred  hours  for  study.  A  part  of  the 
table  is  reproduced  here. 

A.M. 


Hour  

Inds 

6:00 

36 

7:00 
42 

8:00       9:00 
109        137 

P.M. 

A 

10:00 

87 

11:00 
38 

Hour  

Inds 

1:00 

5 

2:00 
2 

3:00       4:00 
2          11 

5:00 
12 

6:00 
5 

In  the  light  of  the  results  we  have  just  obtained,  it  appears 
that  the  subjects'  estimates  of  their  best  hours  are  very  often 
incorrect.  Too  few  chose  the  best  hours,  10  or  11  a.m.  ;  too  many 
chose  too  early  an  hour;  and  very  few  appreciate  the  efficiency 
of  the  afternoon  hours,  noticeably  3  o'clock.  The  conclusion  is 
that  one's  subjective  feelings  with  regard  to  the  time  of  greatest 
efficiency  are  not  reliable  indications   of  real   efficiency.     The 


19161   Gates:  Diurnal  Variations  in  Memory  and  Association     341 

organism  may  be  able  to  produce  the  greatest  amount  and  the 
best  quality  of  work  at  a  time  when  feelings  of  fatigue  and 
kindred  factors  lead  us  to  believe  that  our  efficiency  is  low. 


VIII.  Comparison  with  Eesults  Obtained  by  Other 
Investigators 

The  literature  of  the  subject  of  diurnal  variations  in  efficiency 
can  be  found  in  summarized  form  in  two  monographs.7  But 
briefest  mention  can  be  made  here  of  a  few  of  the  more  extensive 
pieces  of  work. 

Marsh,  in  tests  of  arithmetical  ability,  memory,  attention,  and 
perception,  found  that,  as  a  rule,  the  mid-day  periods  (12:00- 
2:00  p.m.)  were  superior  to  the  afternoon  periods  (4:00-7:00 
p.m.),  which  were  superior  to  the  morning  periods  (7:00-9:00 
a.m.).  Winch8  found  memory  better  in  the  late  forenoon  (9  :45- 
10:05  a.m.)  than  in  the  afternoon  (4:00^:20  p.m.)  ;  and  better 
in  the  afternoon  than  in  the  early  morning.  Robinson,9  in 
arithmetical  work,  found  a  rise  in  efficiency  during  the  forenoon, 
culminating  at  10 :  30  a.m.,  with  a  noticeable  drop  at  12 :  30  p.m., 
and  a  subsequent  rise  until  2:00  p.m.  Hollingworth,10  in  tests 
for  various  functions,  found  a  low  efficiency  at  the  beginning  of 
work,  then  a  gradual  increase  followed  by  a  period  of  low  effici- 
ency. Hollingworth 's  results  and  his  interpretation  of  them  are 
not  in  accord  with  the  present  findings.  The  present  writer,  in 
his  earlier  study,11  obtained  results  from  tests  on  school  children 
which  agree  in  most  respects  with  the  present  findings. 


7  Marsh,  H.  D.,  The  Diurnal  Course  of  Efficiency,  Colum.  Univ.  Contr. 
Philos.,  vol.  14  (1906),  no.  3.  Gates,  A.  I.,  Variation  in  Efficiency  during 
the  Day,  etc.,  Univ.  Calif.  Publ.  Psychol.,  vol.  2  (1916),  no.  1. 

s  Winch,  W.  H.,  Mental  Fatigue  in  Day-School  Children  as  Measured  by 
Immediate  Memory,  Journ.  Ed.  Psych.,  vol.  3  (1912),  pp.  18-29,  75-82; 
Mental  Adaptation  during  the  School  Dav,  Journ.  Ed.  Psych.,  vol.  4  (1913), 
pp.  17-28,  71-84. 

9  Robinson,  L.  A.,  Mental  Fatigue  and  School  Efficiency,  Publ.  Winthrop 
Norm,  and  Indus.  Coll.  S.  C,  vol.  5  (1912),  no.  5. 

io  Hollingsworth,  H.  L.,  Variations  in  Efficiency  during  the  Working 
Day,  Psych.  Rev.,  vol.  21  (1914),  pp.  473-492. 

ii  Loc.  cit. 


342      University  of  California  Publications  in  Psychology     [Vol.  1 

The  curve  of  efficiency  found  by  Robinson,  characterized  by 
an  increase  during  the  forenoon,  a  fall  following  the  lunch  hour 
and  a  subsequent  increase  in  the  afternoon,  is  borne  out  by  the 
present  findings,  as  are  also  the  results  of  Marsh,  showing  the 
superiority  of  the  mid-day  period  over  afternoon  and  morning 
periods,  and  Winch's  results,  showing  a  relatively  great  efficiency 
in  the  late  forenoon.  The  present  piece  of  work  has  produced  no 
evidence  in  support  of  Hollingworth  's  results.12  However,  when 
heed  is  given  to  numerous  factors,  such  as  climate,  habits  of  life, 
the  character  of  tests  employed,  the  methods  of  testing,  and  so  on, 
which  may  differ  with  the  different  investigations,  it  is  not  sur- 
prising that  they  should  lack  entire  harmony.  On  the  contrary, 
the  degree  of  uniformity  which  does  exist  is  surprising. 


IX.  Conclusions 

The  facts  that  have  been  brought  forth  by  this  study  indicate 
the  existence  of  a  diurnal  course  of  efficiency  in  an  important  type 
of  mental  activity.  From  the  early  morning  the  efficiency  of  the 
organism  begins  to  increase,  culminating  in  a  maximum  in  the 
late  forenoon,  followed  by  a  decline  immediately  after  the  noon 
meal,  with  a  subsequent  rise  until  the  middle  of  the  afternoon, 
or  a  little  later,  and  a  final  drop  in  the  late  afternoon. 

Such  is  the  broad  rhythm  found  with  fair  regularity  for 
groups  of  individuals.  But  it  must  be  admitted  that  within  this 
general  trend  exist  numerous  variations  among  the  individuals. 
Differences  in  daily  habits  of  life,  in  the  physical  and  mental 
make-up,  and  in  external  conditions  account,  in  a  large  measure, 
for  such  variations.  Each  individual,  to  profit  most  thoroughly 
from  the  knowledge  of  the  nature  of  his  daily  rhythm  of  efficiency, 
should  determine  it  by  experimental  methods  for  himself. 

The  demonstration  of  such  a  diurnal  rhythm  carries  with  it 
the  suggestion  that  psychological  and  physiological  investigators 


12  Hollingworth 's  results  have  been  discussed  in  the  writer's  earlier 
paper. 


1916]   Gates:  Diurnal  Variations  in  Memory  and  Association     343 

should  take  into  consideration  more  carefully  than  heretofore  the 
fact  of  periodicity  in  individuals.  The  results  of  experiments 
conducted  at  different  hours  of  the  day  are  in  danger  of  being 
disturbed  by  large  errors  due  to  diurnal  fluctuations.  One  who 
reads  the  literature  of  years  of  investigation  for  the  purpose  of 
measuring  mental  fatigue  can  readily  see  the  possibility  that 
diurnal  variations  in  efficiency  have  probably  been  a  prominent 
cause  of  conflict  in  the  findings. 

Yet  the  application  of  the  fact  of  diurnal  rhythms  to  the 
problem  of  fatigue  is  difficult.  This  is  due  to  the  fact  that  the 
curve  of  efficiency,  as  we  have  found  it,  is  influenced  by  the  effects 
of  fatigue,  incitement,  adaptation,  and  other  factors.  The  sub- 
jects working  at  10  a.m.  in  our  experiments  were  doubtless  labor- 
ing under  greater  fatigue  than  those  who  worked  at  8  a.m.,  yet 
in  spite  of  greater  fatigue  their  efficiency  was  higher.  If  they 
had  been  equally  fresh,  their  efficiency  might  have  been  consider- 
ably higher  still.  Just  what  part  fatigue,  feelings  of  fatigue, 
lack  of  interest,  adaptation  and  such  factors  play,  it  is  impossible 
to  say. 

The  fact  is  significant  that  the  hours  of  greatest  efficiency  are 
those  at  which  fatigue,  it  would  seem,  should  be  very  great.  We 
have  found  in  the  present  study,  moreover,  that  most  persons, 
basing  their  judgments  largely  on  their  subjective  feelings,  did 
not  select  as  their  best  hours  for  study  those  which  actually  stood 
highest  in  efficiency  according  to  the  tests.  Thorndike,13  in  sum- 
marizing the  investigations  bearing  on  this  point,  concludes : ' '  The 
feelings  of  fatigue,  from  what  we  know  of  them,  thus  seem  to  be 
a  very  poor  symptom  of  the  loss  of  ability. "  An  opportunity  is 
afforded  us  to  profit  by  such  information.  The  feelings  of  weari- 
ness which  become  more  insistent  as  we  indulge  them  might  be 
made  more  and  more  to  disappear,  provided  the  organism  is  in 
healthy  condition,  if  we  work  on  in  spite  of  them.  A  man  must 
be  trained  to  meet  situations  where  he  must  put  forth  more  than 
the  customary  amount  of  effort.  He  should,  by  practice  in  the 
voluntary  disregard  of  mere  feelings  of  fatigue,  learn  the  limits 


is  Thorndike,  E.  L.,  Educational  Psychology,  vol.  3,  part  1,  p.  107. 


344     University  of  California  Publications  in  Psychology    [Vol. 1 

of  his  ability  and  by  so  doing  attain  greater  assurance,  and,  by 
virtue  of  this,  greater  efficiency. 

The  drop  in  efficiency  following  the  mid-day  meal  has  been 
the  most  consistent  aspect  of  the  curve  that  has  been  found.  No 
exception  to  this  rule  occurs  in  the  case  of  any  function,  and  the 
average  results  show  that  the  minimum  efficiency  of  the  day 
occurs  at  this  hour.  Since  the  returns  for  labor  at  this  time  are 
relatively  so  small,  it  would  seem  that  an  hour  or  two,  following 
the  noon  meal,  could  be  wisely  spent  for  rest  or  recreation. 
Plenus  venter  non  studet  libenter  is  a  maxim  to  which  the  student 
should  give  more  heed.  Such  was  Offner's  firm  conviction  when 
he  wrote:14  "It  is,  accordingly,  one  of  the  most  justifiable  de- 
mands of  school  hygiene  that  the  afternoon  session  .  .  .  should 
begin,  at  the  very  least,  two  hours  after  the  noon  meal,  i.e.,  at 
3  o'clock  and  not  at  2  o'clock."  Such  an  implication  is  not 
altogether  clear,  however,  because  the  exact  causes  of  diminished 
efficiency  at  this  time  cannot  be  accurately  determined.  The 
physiological  effects  of  the  mid-day  meal  are,  perhaps,  not  the 
only  influences  at  work.  It  may  well  be  that  relaxation  or  mere 
cessation  of  work  causes  the  state  of  adaptation,  attained  during 
the  forenoon  exercise,  to  subside;  and  high  efficiency  can  again 
be  attained  only  by  means  of  another  process  of  "warming  up." 
If  such  is  the  case,  the  exact  time  at  which  work  is  renewed  would 
not  be  so  important  a  consideration.  It  was  found,  moreover,  in 
the  earlier  investigation,15  that  efficiency  in  functions  of  the  motor 
type  was  quite  high  soon  after  lunch.  Such  school  subjects  as 
drawing,  painting,  modeling,  writing,  manual  arts  and  the  like 
might  be  profitably  pursued  during  the  early  afternoon  hours. 


14  Offner,  M.,  Mental  Fatigue,  translated  by  Whipple  (1911),  pp.  88-89. 
is  Variations  in  Efficiency,  etc.,  Univ.  Calif.  Publ.  Psychol.,  vol.  2  (1916). 


Transmitted  October  28,  1915. 


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